Insulin injections are traditionally given with either an insulin syringe, usually having an integrated needle permanently or semi-permanently incorporated, or an insulin pen whereby a disposable pen needle is attached to facilitate drug container access and allow fluid egress from the container through the needle into the patient. As technology and competition advance, driving the desire for shorter, thinner, less painful, and more efficacious insulin injections, the design of the needle hub becomes more and more important. Hub designs need to proactively address ergonomically improving injection technique, injection depth control and accuracy, the ability to be safely used and transported to disposal, and protection against misuse while maintaining the ability to be economically manufactured on a mass production scale.
In order to achieve the desired injection depths for shallow subcutaneous and intradermal injections, conventional needle hub assemblies may have a depth-limiting attachment to achieve the desired injection depth, which requires the needle to be longer in length and less structurally resilient to non-perpendicular insertion caused by improper injection technique and general misuse overall.
Needle hub assemblies are typically molded from plastic with a center hole for allowing a needle to pass through the center. The needle is then specially made to the proper injection length on the patient side of the hub for the targeted tissue depth, as well as to have enough length on the proximal or non-patient (NP) side to interface with a medication cartridge. Epoxy or adhesive is then used to secure the needle at the proper length within the center hole. The center hole may be slightly enlarged to form a well for the adhesive to collect and to establish a bond between the needle hub assembly and the needle. FIG. 1 shows a needle hub assembly 1 that includes a cover 10, a needle cannula 31, a needle hub 30, and an inner shield 20. The needle hub 30 also includes a conventional center protrusion 40, an adhesive well 43, and an epoxy or adhesive bump 45 that surrounds the needle cannula 31.
Typically, the adhesive well 43 is overfilled causing the adhesive bump 45 to extend upward from the distal end of the needle hub along the exterior of the needle cannula 31 for a certain length or height. The height of the adhesive bump 45 from one needle assembly to the next is not uniform, but the bumps generally fall within a predetermined maximum tolerance unsuitable for shallow drug delivery. Even within this tolerance the bump reduces the overall effective needle length, to varying extents from needle-to-needle, which can significantly affect depth of medication delivery. Specifically for needles designed with short effective lengths aimed at shallow delivery below the skin, this could affect whether the medication will be delivered to the intradermal tissue layer or the shallow subcutaneous tissue layer.
Other lengths however, can be used. In any case, it is important to provide a hub design which enables tightly-controlled tolerances of needle length (usable) in order to achieve accurate drug delivery specifically targeted to a desired depth. In specific embodiments the delivery is in either the intradermal or shallow subcutaneous tissue.
Other negative effects of the adhesive bump include potential bruising to the patient when administered an injection and producing a single lateral stress point at the needle/bump junction which can cause the needle cannula 31 to more easily bend when used improperly. The bruising caused by the adhesive bump 45 can be caused by the shape of the bump and the force placed on the pen injection device to insure that the needle cannula is fully inserted, and that the injection depth is correct. The effective needle length is important in that as manufacturers attempt to reduce the discomfort associated with injections by manufacturing smaller diameter needles with shorter tightly controlled lengths, the tissue layer in which the medication is injected can vary and the physiologic response becomes more critical. It is important that the injection device be capable of delivering the medication to the targeted tissue layer. Therefore, the effective length of the needle and its associated tolerance is critical in meeting the requirements of the medication dosage and expectations of the user. The user immediately after administering injection may not notice that the medication missed the targeted tissue layer until there is some adverse physical reaction.
Another feature of the needle hub assembly 1 in FIG. 1 is a shield 20 for the proximal or NP end needle point that is exposed when the used needle hub assembly is to be disposed. After the injection has been administered, the needle hub assembly 1 is removed from the medication cartridge (not shown) and prepared for disposal in a biological sharps container or the like. However, at times when a biological sharps disposal container is not available, a user may decide to wait until such a container is available. In the diabetic community, for instance, many times insulin injectors who must give themselves injections while away from home do so with their pen and pen needle and afterward, transport their pen needles home for disposal per their standard, appropriate, sharps disposal means. Typically, if a container for disposal of sharp biological instruments is not available, users of the injection device improperly place the used needle hub assembly in a pocket or purse for proper disposal at a later time, which may result in inadvertent needle sticks during storage, transportation, or disposal of the needle hub. Although the proximal or NP end of the needle 33 does not protrude beyond the outer diameter of the proximal end of the needle hub assembly 30, there is a chance that a person may be pricked by the NP-end 33 of the needle 31 while trying to remove the needle hub assembly 30 from a pocket or purse. Accordingly, the needle hub assembly 1 is fitted with a shield 20 for the NP-end 33 of the needle 31 that requires a snap-fit 35 of the cover 20 over the NP-end needle 33. The snap-fit 35 secures the flange 23 in place. The flange 23 is substantially 90 degrees and is tightly held by the snap-fit 35. The snap-fit 35 is difficult to manufacture and raises the overall manufacturing costs of the device.
An example of an NP-end needle shield is described in commonly-assigned U.S. Pat. No. 5,941,857 to Nguyen et al., the entire disclosure of which is incorporated herein by reference.
Accordingly, a need exists for a disposable injection needle and hub assembly in which the hub provides an effective usable needle length and a non-patient needle end shield.